A battery system according to the present invention includes: a battery module comprising a plurality of cell groups connected in series, each comprising a plurality of cells connected in series; a plurality of integrated circuits provided to corresponding each cell group of the battery module, that perform detection of terminal voltages of the cells in the corresponding each cell group, and that also perform diagnosis; and a battery controller that, along with issuing commands to the plurality of integrated circuits, also receives results of detection and results of diagnosis by the plurality of integrated circuits; wherein the battery system comprises a writable non-volatile memory, and data is stored in the writable non-volatile memory specifying usage environment of the battery module, including a maximum voltage or a maximum current of the battery module and history data based upon operation history of the battery module.